# trunc, truncf, truncl

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< c‎ | numeric‎ | math

Defined in header ``<math.h>`` |  |
float truncf( float arg ); | (1) | (since C99)
double trunc( double arg ); | (2) | (since C99)
long double truncl( long double arg ); | (3) | (since C99)
Defined in header ``<tgmath.h>`` |  |
#define trunc( arg ) | (4) | (since C99)

1-3) Computes the nearest integer not greater in magnitude than arg.
4) Type-generic macro: If arg has type long double, `truncl` is called. Otherwise, if arg has integer type or the type double, `trunc` is called. Otherwise, `truncf` is called.

### Parameters

arg | - | floating-point value

### Return value

If no errors occur, the nearest integer value not greater in magnitude than arg (in other words, arg rounded towards zero), is returned.

Return value
Argument

### Error handling

Errors are reported as specified in `math_errhandling`.

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

- The current rounding mode has no effect.
- If arg is ±∞, it is returned, unmodified.
- If arg is ±0, it is returned, unmodified.
- If arg is NaN, NaN is returned.

### Notes

FE_INEXACT may be (but isn't required to be) raised when truncating a non-integer finite value.

The largest representable floating-point values are exact integers in all standard floating-point formats, so this function never overflows on its own; however the result may overflow any integer type (including intmax_t), when stored in an integer variable.

The implicit conversion from floating-point to integral types also rounds towards zero, but is limited to the values that can be represented by the target type.

### Example

Run this code

    #include <math.h>
    #include <stdio.h>

    int main(void)
    {
        printf("trunc(+2.7) = %+.1f\n", trunc(+2.7));
        printf("trunc(-2.7) = %+.1f\n", trunc(-2.7));
        printf("trunc(-0.0) = %+.1f\n", trunc(-0.0));
        printf("trunc(-Inf) = %+f\n",   trunc(-INFINITY));
    }

Possible output:

    trunc(+2.7) = +2.0
    trunc(-2.7) = -2.0
    trunc(-0.0) = -0.0
    trunc(-Inf) = -inf

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.12.9.8 The trunc functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.6.8 The trunc functions (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.9.8 The trunc functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.6.8 The trunc functions (p: TBD)

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.9.8 The trunc functions (p: 253-254)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.6.8 The trunc functions (p: 528)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.9.8 The trunc functions (p: 234)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.6.8 The trunc functions (p: 464)

### See also

floorfloorffloorl (C99)(C99) | computes largest integer not greater than the given value (function)
ceilceilfceill (C99)(C99) | computes smallest integer not less than the given value (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99) | rounds to nearest integer, rounding away from zero in halfway cases (function)
C++ documentation for trunc

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